The present invention relates to an improved chemical polishing bath for metal brightening. More specifically, the present invention relates to an improved composition and method for chemical polishing of copper and copper alloy substrates.
Chemical polishing or brightening of copper alloy substrates, electroplates and the like has been known in the art for preparing surfaces for further plating thereover and/or commercial grade polish. Typical bright dipping baths include mixtures of one or more acids such as concentrated sulfuric, phosphoric, nitric, hydrochloric, acetic and chromic acids. These baths, while having tendency to brighten the copper, are hard to control and result in unwanted etching of the copper if not utilized under strict process parameters.
In recent years, the use of hydrogen peroxide as an additive to acid brightening baths has greatly increased the stability and useability of these baths. However, hydrogen peroxide rapidly degrades in such acid solutions, and typically, such solutions typically include additives such as chelating agents and chromic acids which require special costly treatment of disposal. While these brightening baths provide superior brightening of copper substrates, they have a disadvantage in that the drag-out of chromic acid into the rinse bath is so great that at times parts will be etched in the rinse water. While other additives are known to provide advantageous brightening at reduced chromium levels, there still remains a need in the art for improvement through removal of chromic acid content, while providing better bath stabilization, improved levelling and reduced etching of parts, such that only high quality brightening is achieved.